The invention relates to an incandescent lamp with at least one incandescent coil which can be used for generating a high beam in a motor vehicle headlight, by means of which lamp in addition the function of a daytime running light can be performed.
Many traffic accidents are caused by an insufficient visibility of the vehicles taking part in the traffic also in daylight. To avoid accidents, motor vehicles may accordingly be provided with so-called daytime running lights (DRL). The daytime running light must be designed such that the vehicle can be better observed by others taking part in the traffic without causing any serious annoyance (for example by dazzling). The activation of such a daytime running light may preferably be coupled to given ambient parameters such as, for example, the ambient light level and motor running, in which case it will be permanently switched on. The moment the ambient light falls below a certain value, a switch is to be made from the daytime running light to the low beam. Furthermore, the daytime running light is also switched off when the motor is merely stationary, in particular so as to reduce the power consumption. The requirements for a daytime running light are similar to those for the main beam of a motor vehicle headlight as regards the symmetrical alignment to the horizon. However, the requirements for the light distribution and intensity are strongly different. The intensity is substantially lower and horizontally more widely distributed. In contrast to a comparatively sharp focusing on the horizon (the so-called HV point on the reference axis), the daytime running light has to be wider and flatter. The requirements imposed on the daytime running light (DRL) are laid down in law in a similar manner as for the low beam and the high beam. In addition, a daytime running light must have a long life and a low power consumption.
Known solutions for the realization of a daytime running light function are based on a reduction of the voltage for headlights already present (dimming). Dimming of the existing incandescent lamps leads to a substantial loss in luminous efficacy because the proportion of visible light generated in relation to the total power consumption of the incandescent lamp drops sharply. This causes a strongly increased power consumption which leads also to an undesirable increase in fuel consumption of the motor vehicle. Another aspect of the realization through dimming of the light is that the light distribution thereof is mainly directed at the street because of legal requirements, so as not to dazzle oncoming drivers in darkness. This distribution remains intact also in the dimmed state, so that only a small portion of the light contributes to the improvement of visibility for other persons taking part in traffic. A daytime running light realized in this manner accordingly has a low efficacy and is not suitable as an energy-saving daytime running light (DRL). The use of a dimmed high beam as a daytime running light also has the disadvantage of a light distribution of the high beam which is unsuitable for the function of a daytime running light. Since the high beam is too sharply focused, the distribution of the luminous intensity of a high beam does not comply with the legal requirements for a daytime running beam. In addition, the high beam, if it is to comply with the requirements as regards the maximum luminous intensity of the daytime running light, would have to be dimmed to such an extent that the halogen cycle in the bulb of the incandescent lamp can no longer be maintained. This leads to blackening of the bulb inside and a shortening of lamp life.
The patent document U.S. Pat. No. 5,614,788 discloses an automated daytime running light system which reacts to ambient conditions. The automated daytime running light system for motor vehicles with front lights comprises a circuit for controlling the daytime running light which supplies the incandescent coil for the main beam with a reduced voltage whenever the ignition of the motor vehicle is switched on and the starter is switched off in daylight. Such a daytime running light system realized by means of a high beam has the known disadvantages.
The German patent document laid open to public inspection DE 195 10 542 furthermore, discloses a headlight circuit which is capable of carrying out a switch-over between a normal headlight, a low-beam headlight, and a daytime running light (DRL) by means of a multiple control circuit without a substantial change in the wiring in a cable harness. In spite of a possible simplification in the wiring in the cable harness upon the switch-over of the headlight, the daytime running light created through dimming has the known disadvantages.
It is accordingly an object of the invention to provide an incandescent lamp which renders possible an improved realization of a daytime running light function in a motor vehicle headlight.
This object is achieved in that the incandescent lamp comprises at least a first incandescent coil for generating a high beam in a motor vehicle headlight and at least a second incandescent coil for generating a daytime running light in a motor vehicle headlight.
The combination of the second incandescent coil with the incandescent coil for the high beam leads to a lamp which offers the functions of a high beam and of the daytime running light in a surprisingly simple manner. The integration into one incandescent lamp according to the invention provides the possibility of use in various motor vehicle headlights without detracting from any existing functions. The motor vehicle headlight need not be newly designed for this, but it can continue to be used with an adapted reflector.
In an advantageous further embodiment of the incandescent lamp according to the invention, an incandescent coil with a power of at most 30 W is provided for forming the second incandescent coil. The daytime running light can be optimized through a suitable choice of the diameter, length, material, and other parameters for the second incandescent coil which generates the daytime running light. In particular, the incandescent coil will be so designed that a maximum luminous efficacy (quantity of light generated per unit power lm/W) of the lamp is achieved at a power of approximately 20 W (maximum 30 W). A value of approximately 20 W is regarded as favorable for a daytime running light in view of the requirements (in particular legal requirements). For comparison, the first incandescent coil usually has a power of 65 W for generating the high beam.
In a preferred embodiment of the invention, the second incandescent coil is arranged so as to lie on the axis of the first incandescent coil. The second incandescent coil may be arranged behind or in front of the first incandescent coil, as viewed from a cap of the incandescent lamp. The arrangement of the two incandescent coils on one common optical axis offers good possibilities for realizing a reflector in which the incandescent lamp can be accommodated and which generates a suitable high beam as well as a daytime running beam in a headlight unit. Alternative arrangements of the two incandescent coils in a bulb of the incandescent lamp are indeed possible within the scope of the invention, if the requirements of a given application make a different arrangement seem more favorable (for example, parallel next to one another, or at right angles to one another). These requirements may be, for example, legal requirements imposed on the headlight into which the incandescent lamp is to be incorporated or on the incandescent lamp itself. Particular requirements may also arise on the basis of the manufacturing process.
In an embodiment of the invention, a first electrical current lead is provided to a first connection of the first incandescent coil, a second electrical current lead is provided to a first connection of the second incandescent coil, and a third electrical current lead is provided to a second connection of the first and of the second incandescent coil, the leads passing through the lamp cap.
Further advantageous embodiments of the invention are defined in the further dependent claims.